Gaseous support bed for conveying and heat treating glass sheets



Aug. 29. 1967 H. A. M MASTER ETAL GASEOUS SUPPORT BED FOR CONVEYING ANDHEAT TREATING GLASS SHEETS 5 Sheets-Sheet 1 Original Filed Nov. 29, 19635 Sheets-Sheet 2 Hun 29. 1967 H. A. M MASTER ETAL GASEOUS SUPPORT BEDFOR CONVEYING AND HEAT TREATING GLASS SHEETS Original Filed Nov. 29,1963 zoEwz E @355 5%: 53:58 kzfiwzou wwmzmsm @539 0? 1* bmdi ow u be: mm v 0 m m 3 H. A. M MASTER ETAL GASEOUS SUPPORT BED FOR CONVEYING ANDHEAT TREATING GLASS SHEETS Aug. 29, 1967 5 Sheets-Sheet 3 Original FiledNov. 29, 1963 29, 1%? HA M MASTER ETAL swam? GASEOUS SUPPORT BED FORCONVEYING AND HEAT TREATING GLASS SHEETS 5 Sheets-Sheet 4,

Original Filed Nov. 29, 1963 I ram/5w 29. 1967 H. A. M MASTER ETAL3,338,697 GASEOUS SUPPORT BED FOR CONVEYING AND HEAT TREATING GLASSSHEETS Original Filed Nov. 29, 1963 5 Sheets-Sheet 5,

R o 6 o 0 I N VENTOR5 United States Patent 3,338,697 GASEOUS SUPPORT BEDFOR CONVEYING AND HEAT TREATING GLASS SHEETS .Harold A. McMaster,Woodville, and Norman C.

Nitschke, Perrysburg, Ohio, assignors to Pennaglass, Inc., Woodville,Ohio, a corporation of Ohio Original application Nov. 29, 1963, Ser. No.326,713. Divided and this application Sept. 15, 1966, Ser. No. 579,628

12 Claims. (Cl. 65-182) ABSTRACT OF THE DISCLOSURE The instant inventionrelates to an integral ceramic block to form a bed in a glass treatingfurnace where sheets of glass are floated on fluid over the bed whilebeing treated and, more specifically, to such a block including firstand second surfaces interconnected by a plurality of sides with a firstplurality of passages extending through the interior of the block, asecond plurality of passages extending completely through the blockbetween the sides thereof and a third plurality of passages extendinginto the block from the first surface and communicating with the secondplurality of passages so that fluid may pass through the first pluralityof passages to the first surface, laterally over the first surface, andout through the second and third plurality of passages to the sides ofthe block.

This application is a division of application Ser. No. 326,713, filedNov. 29, 1963, in the names of Harold A. McMaster and Norman C. Nitschkeand assigned to the assignee of the instant invention.

In recent years there has been a greatly increased demand for curvedglass sheets or plates for use as automobile windows, protective windowsfor television screens, architectural glass, etc. Also, there has beenever increasing recognition of the advantages of tempered glass,particularly its high strength and safety features. Currently, the bigdemand is for windows of relatively thin tempered curved glass. Tomanufacture tempered glass it is necessary that the individual glasspieces first be cut and to the particular shape desired and thentempered. Hence, to manufacture curved tempered glass automobile windowsor the like, the essential sequence of steps is 1) form an untemperedglass sheet to proper size, with edges rounded and polished as desired,(2) heat and bend the sheet to the curvature required, and (3) rapidlyand uniformly cool the curved sheet to provide the temper.

The stock method for bending a glass sheet to curved or bowedconfiguration is to heat the glass sheet to its softening temperatureand then press or allow it to sag under gravity against a mold havingthe curved or bowed shape desired. Flat glass is suspended on tongs orracks during the heating process. However, these methods have seriousdisadvantages, perhaps the chief of which is that of marring of theglass, particularly at the edges thereof, by contact with the mold ortongs. This is particularly a problem for the manufacture of temperedglass since, once tempered, surface imperfections cannot be easilycorrected. Another serious disadvantage of these methods is that theyare inherently ill suited to large scale production since the glasspieces must be made one at a time rather than on a continuous basis. Thesolution proposed by the prior art for the marring problem is to providea cushion of gas between the softened glass surface and the mold.Numerous patents show this concept or variations thereof, U.S. Patent2,395,727, Devol, being typical. Various other prior patents teach thata gas film support is not only useful to prevent marring but also as asubstan- 3,338,697 Patented Aug. 29, 1967 ice are US. Patent 1,591,179,Myers; 1,622,817, Waldron;

1,821,375, Brancart; and 2,505,103, Devol. This suggests then that toform curved glass sheets on a continuous high production basis, it isonly necessary to heat and float the sheets on a film of hot gas acrossa bed which provides the precise curvature desired. In practice,however, such method presents numerous problems, particularly as regardsthe manufacture of high quality tempered glass sheets. One problem, forexample, is that of attaining the almost perfect uniformity of heatingof the glass sheets which is required in order to attain the desiredcurvature but without localized distortion to the glass surface. Anotherproblem is that of preventing any contact of the glass sheets with thesupport bed, particularly in that zone on the bed where the glasschanges from flat to curved shape. It is in this transition zone wherecontact is most likely to occur. Another problem is that of transportingor guiding the softened sheets across the bed without at the same timecausing marring or distortion of the glass because of contact with theguide or transport means. Another problem perculiar to the manufactureof tempered glass is that of attaining a uniform temperature prior totempering and optimum uniformity in cooling during tempering to preventwarpage or shattering. A further problem which is extremely importantfrom the practical standpoint is that of accomplishing such an apparatuswhich can be constructed, operated, and maintained at relatively lowcost. The chief difliculty here is that the furnace bed on which theglass sheets float must inherently be of considerable length and mustoperate at high temperature, sufficient to soften the glass. This leadsto thermal expansion problems and attendant stresses and distortions inthe support bed. Any such distortions are, of course, a seriousimpairment since the attainment of an accurate, controlled glasssurface, be it curved or fiat, is dependent upon perfect accuracy of thebed surface. Additionally, distortion in the bed can result innon-uniform flotation of the sheets and resultant contact between thesheets and the bed causing marring of the glass. These, then, are someof the more serious difficulties which must be solved in order toprovide an eflicient, relatively low-cost apparatus formanufacturingtempered glass sheets, and particularly curved tempered sheets, by amethod wherein the sheets-are heat softened while being gas floatedovera bed which is shaped to provide the desired contour. The presentinvention solves these difliculties.

Hence, it is a principal object of the present invention to provide animproved method and apparatus for manufacturing sheets of glass or thelike efficiently and at relatively low cost. More specifically, it is anobject of the invention to provide a glass manufacturing apparatus ofthe type described whereby tempered curved glass sheets of exceptionallyhigh quality can be manufactured on a continuous high production basisat relatively low cost with very low scrap or breakage losses. Thesealong with other objects, features and advantages of the invention willappear more clearly from the following detailed description of apreferred embodiment thereof made with reference to the drawings inwhich:

FIGURE 1 is an isometric view, with parts broken away and partiallyschematic, of the preferred apparatus and illustrates the bedconfiguration into and through the heating furnace wherein the glasssheets are curved, and into and through the blasthead wherein the curvedglass sheets are tempered;

FIGURE 2 is a schematic elevational view within the furnace to show thecontour of the bed and the various furnace zones;

FIGURE 3 is a partial longitudinal cross sectional view of the furnaceof FIGURES 1 and 2 illustrating the position of the various parts invarious zones;

FIGURE 4 is a transverse cross sectional view of the furnace of FIGURE 1taken substantially along the line 4-4 of FIGURE 3 and looking in thedirection of the arrows;

FIGURE 5 is another transverse cross sectional view of the furnace ofFIGURE 1 taken substantially along the line 55 of FIGURE 3 and lookingin the direction of the arrows;

FIGURE 6 is a perspective view of a portion of the bed wherein the bedcontour is flat;

FIGURE 7 is a perspective view of another portion of the bedillustrating the position of the inlet and exhaust openings therein;

FIGURE 8 is a plan view of the portion of the bed illustrated in FIGURE7 showing the position of the inlet and outlet passages;

FIGURE 9 is a cross-sectional view of the bed portion of FIGURE 7 takensubstantially along the line 9-9 of FIGURE 8 and looking in thedirection of the arrows;

FIGURE 10 is a transverse cross sectional schematic view of theblasthead at the end of the furnace illustrated in FIGURE 1;

FIGURE 11 is an enlarged cross sectional view of the portion of theblasthead illustrating the construction of the upper and lower blastheadbeds;

FIGURE 12 is a plan view of a portion of the blasthead lower bed takensubstantially along the line 12-12 of FIGURE 11 and looking in thedirection of the arrows;

FIGURE 13 is an enlarged longitudinal cross sectional view of a portionof the blasthead lower bed taken substantially along the line 13-13 ofFIGURE 12 and looking in the direction of the arrows;

FIGURE 14 is a side view of a portion of the upper and lower blastheadbeds taken substantially along the line 14-14 of FIGURE 11 to illustratethe flow regulation means;

FIGURE 15 is a cross sectional view of a portion of the conveyor meansextending along one side of the furnace of FIGURE 1 illustrating theposition of the various parts;

FIGURE 16 is a plan view of the conveyor system and conveyor supportfoot taken substantially along the line 16-16 of FIGURE 15 and lookingin the direction of the arrows;

FIGURE 17 is a partial elevational view of a portion of the conveyorchain of FIGURES 15 and 16;

FIGURE 18 is a schematic view of a portion of the bed assembly andconveyor means showing the position of the glass sheets fortransportation across the bed;

FIGURE 19 is a perspective view of a glass sheet such as might betreated in the furnace illustrated in FIG- URE 1 and wherein the axis ofthe curvature is parallel to the edge of the sheet;

FIGURE 20 is a schematic view of a portion of the bed assembly showingglass sheets in another portion for transportation across the bed andthrough the furnace of FIGURE 1;

FIGURE 21 is a perspective view of a glass sheet such as might betreated in the furnace of FIGURE 1 and with the axis of curvatureangularly disposed relative to the edge of the glass sheet.

Referring more particularly to FIGURE 1, the apparatus shown comprisesan elongate perforated bed, illustrated generally by the numeral 20which, in the actual embodiment herein shown, is about 180' feet longand is composed of three main sections. These sections include a loadingsection 21, a heating and bending section 22, and a tempering section23. The heating and bending section 22 is within and constitutes thefloor of an elongate furnace structure, illustrated generally by thenumeral 24, and the tempering section 23 extends through a cool- 4 ingblasthead, illustrated generally by the numeral 25. The bed is flatthroughout section 21 and most of section 22; and approximatelytwo-thirds of the way through section 22 gradually becomes curved in adirection transverse to the longitudinal axis of the bed. Bed section 23within the blasthead 25 and the portion of section 22 toward the end ofthe furnace adjacent the blasthead have a uniform transverse curvaturesubstantially the same as that desired of the glass sheets to bemanufactured. The plane of the bed is tilted about the longitudinal axisthereof at a slight angle to the horizontal, preferably from about 3 to12, and hence the left longitudinal edge of the bed, as shown at 26, islower than the right edge 27. A chain conveyor system, illustratedgenerally by the numeral 28, carrying spaced pairs of glass sheetsupport pads 22, serves to move the glass sheets over the bed 20 fromthe loading section 21 through the furnace 24 and through the blasthead25. Gas emitted from perforations in the bed 20 provides a film orcushion of gas on the bed for flotation of the glass sheets thereover ina manner to be described in detail hereinafter. In essence, then, andwithout attention at this time to important features and details, theapparatus operates as follows: The glass sheets '30 to be curved andtempered are placed onto the bed at loading section 21 with the bottomedge of each sheet resting on a pair of pads 29 secured to the conveyorchain 28. The glass sheets are conveyed by the chain and float over thebed out of contact therewith by reason of the gas emitted from theperforations in the bed. The floating glass sheets are thus guidedthrough the furnace 24 where they are heated to deformation temperatureby the hot gases emitted from the bed perforations and as they reach thecurved portion of section 22, the sheets sag under gravity to conform tothe curvature thereof, all the while supported on gas out of contactwith the bed. Hence, when the sheets reach the end of the furnace, theyare shaped with the full curvature desired. Transportation of thefloating heated curved glass sheets then continues through the blasthead25 where they are tempered by the cooling air projected from the bedperforations in the blasthead.

Support bed structure As alluded to previously, one of the more seriousdifficulties with apparatus of the general type described is that ofthermal expansion of the bed within the furnace. Since it is generallyundesirable to raise the temperature of the glass sheets too rapidlylest there be non-uniform heating with resultant damage to the glass andsince a high rate of production is desired, it will be manifest thatthere are advantages to using a furnace of considerable length; in theembodiment shown it is about feet long. The furnace operates at atemperature upwards of 1100" F. and as high as 1350 F., and differenttemperature zones are maintained within the furnace, as will behereinafter described. Initially and after any maintenance shutdown, thefurnace must, of course, by taken from room temperature up to theseoperating temperatures and yet if there is uncompensated thermalexpansion of the bed through its 140 foot length, bed distortion willresult and this in turn leads to non-uniform glass flotation, poor heatdistribution, marring of the glass due to contact with the bed,inaccurate glass curvature, and other problems. Of course, one waytominimize the problem of glass contact with the bed is to float theglass rather high off thebed by using considerable gas pressure;however, this is inherently expensive in that higher pressures involvehigher costs, and it also has the serious disadvantage of affording lesscontrol over the precise shape imparted to the glass sheets. As will bedescribed hereinafter, in the preferred system of the present inventionthe glass sheets float at an extremely low stable level over the bed,particularly just prior to and while the glass is curved, and this makesit all the more essential that there be no distortion in the bed as canresult from thermal expansion.

In accordance with the invention, the entire bed section 22, is formedof material having an extremely low coefficient of thermal expansion notmore than 1 10 C., as well as excellent heat shock resistance,sutlicient that the bed when at a temperature as high as about 1350" F.can be exposed to room temperature air without damage to the bed. Morespecifically, the bed section 22 in the furnace 24 is formed of fusedquartz blocks 31, each of which has a width equal to the width of thebed and a length of about 30 inches. Hence, the entire 140-foot bedsection 22 comprises fifty-six of the quartz blocks 31 axially alignedand in abutting relationship and preferably with a smooth powdered fusedquartz caulking filling any crevices therebetween to seal and cement theblocks together. The blocks are manufactured by casting and then firingto sintering temperature granular fused quartz preferably of variatedgrain size. That is, quartz powder having a grain size of 325 mesh andfiner is admixed with water to form a slurry and into this can be mixedgranular quartz of varying size, from 200 mesh up to inch, such mixturethen being cast to the shape desired in a porous plaster mold or thelike. After drying, the cast blocks are then fired to about 2000 F. tocause sintering, as is well known in the art. Preferably, the blocks arecast with the overall curved or other surface configuration desired andwith at least the larger of the gas passages therein and, after firing,are machined to their precise final shape. Such blocks have so low acoefiicient of thermal expansion, about .54 10 C. that the overalllinear expansion of the full 140-foot bed in going from room temperatureto 1200 F. is less than 1 inch and the expansion across the width of thebed and through the thickness of the bed is so little as to benegligible. Further, the fused quartz bed has extremely high heatresistance, erosion resistance, and heat shock resistance and thereforelasts indefinitely with practically no maintenance. Because of itssuperb thermal shock resistance, there is no danger of breakage in thebed even though when at a temperature of 1350 F. or so it is exposed toroom temperature air, for example, in the case of an emergency furnaceshut down. Because glass does not adhere strongly to the quartz, ifsoftened glass should contact it and become hardened thereon, as in thecase of a blower or power system failure or the like, it can be quiteeasily removed. As a still further advantage, the quartz bed is quiteinexpensive to manufacture and install. While fused quartz ceramic asdescribed is outstandingly superior it will be understood that othermaterials can be used for the bed. For example, nucleated glasses suchas Pyroceram marketed by the Coming Glass Company, and various highalumina and/or high m ullite ceramics known to have good thermal shockresistance and low coefiicients of thermal expansion as well as goodheat and erosion resistance can be used if desired, though not to thesame advantage as fused quartz.

In the particular embodiment shown, the loading section 21 of bed isfor-med of aluminum sheets 32; though if desired, it can be made ofWood, plastic board or the like. The use of ceramic for the bed section21 has no advantage and, in fact, is disadvantageous because of cost ascompared with sheet aluminum or plastic and also because of the greaterpossibilities of injury to the glass during the loading operation. Inthe particular embodiment shown, the bed section 23 in the blast-head 25is likewise made of aluminum sheet 33. However, for some embodiments itwill be advantageous to use a bed material in the blasthead the same asthat described for use in the furnace for two important reasons. 'First,because fused quartz, or other ceramic, has very low heat conductivityas compared with aluminum or other metal, there is little possibility ofchill cracks developing in the glass sheets by reason of contact of theglass with the blasthead bed. With the threat of such glass damageeliminated, there is less need for absolute assurance against glasscontact with the blasthead bed thus simplifying blasthead design.Secondly, the excellent heat shock resistance of the ceramic assuresagainst bed damage in the case of hot and then cold gas impinging on theblasthead in rapid succession, as can occur in that portion of theblast-head adjacent the furnace. Further, the dimensional stability ofthe ceramic through a wide temperature range, from room temperature towell above 1350 F., assures maintenance of a perfect alignment betweenthe bed surface in the furnace and that in the blasthead thereby betterassuring against contact of the glass with the bed. Using a fused quartzbed in the furnace and the blasthead it is possible and in factadvantageous to have a single bed block span the line of separationbetween the furnace and the blasthead thereby absolutely assuringperfect bed alignment at this point. The high thermal shock resistanceof the ceramic allows this without hazard of injury to the material byreason of the great temperature differential between the furnace and theblasthead.

As indicated above, the quartz bed section 22, albeit it has anextremely low coefficient of expansion, does expand very slightly on itslongitudinal axis when heated to operating temperature. At the sametime, however, the metal support structure of the furnace expandsconsiderably when the furnace 24 is heated to operating temperature.Though it forms no part of the instant invention, it is appropriate tomention that in the embodiment shown compensation is made for this bysupporting the bed on a support structure which is independent of thefurnace whereby the furnace can expand without stressing the bed, thebed support being so constructed and positioned that its thermalexpansion, in its temperature environment, is quite low and about thatof the bed when the latter is heated to operating temperature. Suchsupport structure is disclosed and covered in United States patentapplication Ser. No. 328,393 filed Dec. 5, 1963, now Patent No.3,281,229 in the name of Harold McMaster and assigned to the assignee ofthe present invention.

In the embodiment of the invention shown in the accompanying drawingsand described in detail herein, the glass sheets are treated to formcurved glass sheets typical of what might be used in automobile sidewindows or the like. Under such conditions it is of course necessarythat the bed 20 be curved at some point into the desired glaSS contour.For proper treatment of the glass sheets, the bed contour should notchange too rapidly, nor change to the desired curvature :before theglass sheet is raised to deformation temperature. Hence it is that thebed 20 has a flat upper surface over most of its length, in order toprovide suflicient time for the glass sheets to reach deformationtemperature, and in a zone toward the end of the furnace the bed surfacecontour changes gradually from the flat to curved. At the end of thefurnace and into the blasthead, the contour of the bed 20 is such as toprovide the curvature desired in the glass sheets. However, as alludedto previously, it is to be understood that the apparatus and method ofthis invention is not restricted to use for curving glass sheets, butmay also be used for other glass treatments as well. For example, thefurnace construction, but with the entire bed fiat, may be used fortempering flat glass sheets, or it may be used for coating or annealing.In fact, the apparatus and method may be used for any treatment of sheetmaterial wherein gas flotation is desirable and particularly when thesheets must additionally be heated.

Referring again to the structure of support bed 20, it will be notedfrom the various figures of the drawings that the bed sections areprovided with a plurality of holes or perforations of varying patterns,size, and location. The purpose for this will become hereinafter moreapparent, but for present purposes sufiice it to say that theperforations permit the flow of gases through the bed to provide optimumsupport and heating of the glass sheets as they pass thereover. Alongthe major portion of the length of bed 20 there are only gas inletpassages extending through the various bed sections. In that portion ofthe bed where the glass has reached its deformation temperature andwhere the surface contour is curved, both inlet and exhaust passages areprovided. The size, number and location of the passages permits the useof a low pressure flow system of recirculating gases to float the glasssheet over the bed and through the furnace.

Heating system As has now become apparent, the method and apparatusdescribed and shown herein makes use of an elongated furnace which inthe embodiment shown is of generally box-like construction. The furnacewalls and support structure can be of design well known in the art. Itis of course desirable that the furnace be fully insulated and that thestructural parts of the furnace be subjected to as little heat aspossible to avoid expansion and contraction problems as the furnace israised to the desired temperature. To this end, the furnace 24 may beconstructed with top and bottom walls 34 and 35 and opposite side walls36 and 37 having insulating material 38 disposed on the inner surfacesthereof. Structural support posts 39 and lateral supporting members 40may be provided in any suitable manner and suitably anchored to supportthe remainder of the furnace, it being desirable to keep the posts 39and stringers 40 outside of the insulating means 38 to eliminateexpansion and contraction problems.

In order to provide heat within the furnace 24, a plurality of burners,illustrated generally by the numeral 41, are provided, in varyingnumbers and varying distances from the bed 20 disposed within thefurnace, for purposes to become hereinafter more apparent. The burners41 may be of any suitable type sufficient to provide the proper amountof heat and to operate on a convenient fuel, such as a gas and airmixture. The burners receive the fuel and air mixture through aconventional piping system, not shown. Radiant burners which burn at atemperature of about 2000 F. and which are well known in the glassprocessing furnace art are preferred.

Referring now to FIGURE 2, a schematic cross sectional view of thefurnace is shown, and indicated thereon are various zones numbered 1through 14. As has been previously alluded to, the embodiment of thefurnace shown is 140 feet along; and thus each zone represents feet ofthe furnace. In zones 1-7 inclusive, the burners 41 depend from theceiling of the furnace toward the bed support 20. The number andlocation of the burners is such as to raise the temperature in thefurnace 24 to a temperature of from 1200 F. to 1350 F., depending, ofcourse, upon the type of operation to be carried out in the furnace.From what has thus far been stated it should be clear that for optimumoperation of the apparatus it is important that the glass sheets floatuniformely out of contact with the bed and, where the glass sheets areto be curved as in the embodiment shown, that nothing interfere with thesagging of the heat softened sheets by gravity so as to conform to thebed curvature. To the end of accomplishingsuch optimum performance ithas been found highly desirable to provide means in the furnace foraccelerating the heating of the top surfaces of the glass sheets, atleast prior to that zone in the furnace where the curvature begins, zone11 in the embodiment shown. Hence, as can be seen in FIGURES 1 and 5,the burners 41 in zones 1 to 1% are spaced more closely to the supportbed than are the burners in the remainder of the furnace. Such burners,i.e. the burners in zones 1 to 1th, by reason of their lowered positioncause the hot combustion gases to actually play against the uppersurfaces of the glass sheets thereby serving as the means to acceleratethe heating of such surfaces. If desired, only those burners in zonesabout 8 to 1% (i.e., the zones immediately preceding that wherein thecurvature begins) can be lowered, those in zones 1 to 6 being positionedhigher; however, this will not serve to equal advantage for reasonswhich will be apparent from the following. If a glass sheet is heatedmore rapidly on one side than the other warpage inherently results. Thisis because glass is a poor heat conductor, considerable time beingrequired for the heat imparted to one side to be transferred through theglass to the other side. Further, it will be clear from the foregoingdescription that in the apparatus shown, the flotation system for theglass sheets inherently and intentionally results in a relatively rapidheating of the bottom surfaces of the glass sheets, the flotation gasesemitted from the bed being hot. In the absence of any means for heatingthe top surfaces of the glass sheets at a commensurate rate, warpagewill therefore generally result and such warpage can and does occurabout an axis transverse to the bed, the front and back edges of thesheet being high and the middle low. If such warpage is not corrected atleast by the time the sheet reaches the zone where bed curvaturecommences, it can seriously interfere not only with the gravity saggingof the sheet into conformity with the bed but also with flotation. Thisis because the axis of warpage curvature is at right angles to the axisof bed curvature and hence even though the sheet is at deformationtemperatures, it cannot freely sag to the curved contour of the bed. Andnot being able to conform to the bed, uneven spacing between the sheetand the curved bed results across the surface of the sheet therebydisrupting proper flotation and greatly increasing the possibility ofglass contact with the bed. Hence, it is that it is highly desirable atleast prior to the curvature zone to accelerate the heating of the uppersurfaces of the glass sheets such that by the time the sheets reach thecurvature zone, there is substantially no temperature gradient throughtheir thickness and hence no warp to interfere with proper sagging andflotation. Of course, ideally warpage should be prevented or at leastinhibited from the outset, throughout the furnace, and it is for thisreason that lowered burners are used in Zones 1 through 10 rather thanin just those zones immediately preceding that wherein bed curvaturebegins. It will be of interest to note, however, that if for any reasonit is not desirable or convenient, to use lowered burners or other meansin zones 1 through 7 to accelerate heating of the upper surface of theglass sheets commensurate with the rate of heating of the bottomsurfaces, the flotation system of the present invention is such that itpermits this. That is, as will be brought out hereinafter, the floatsystem is such that the sheets float relatively high in the early zonesand hence, even though the sheets be warped in these zones there islittle, if any, likelihood of contact between the glass and the bed dueto warpage so long as the warpage is sufliciently corrected before thesheets reach the bed curvature zone.

In effect then, the burners are lowered to increase the rate of heatingof the upper surfaces of the glass sheets by radiation and byimpingement of the hot combustion product gases to thereby balance theheating rate to that of the bottom surfaces which is accelerated due tothe impingement of the hot flotation gases. It will be understood thatmeans other than lowered burners can be used if desired to accomplishsuch end. For example, burners or other heating means can be locatedremote from the glass and by means of a blower or the like the hot gasestherefrom directed as by nozzles against the upper surfaces of the glasssheets, similar, for example, to the arrangement now to be describedWith reference to the last zone, zone 14, of the furnace.

In zone 14 it is desirable to cool the glass sheets before entry to theblasthead 25 by lowering the zone temperature to approximately 1150 F.,or about to 200 less than the temperature of the previous zone. Thecooling process is gradual, and uniformity of cooling through thethickness of the glass is accomplished through the use of upper jets of1100 to 1150 F. gas which play against the upper surface of the glasssheets to cool the upper surfaces at about the same rate as the lowersurfaces are cooled by the l100 to 1150 F. flotation gas emitted fromthe bed. For purposes herein it is sufficient 9 to note that the coolingmeans 42 brings the temperature of the glass sheets from the deformationtemperature of about 1250 to 1350 F. to a lesser temperature to initiatethe tempering process which is completed in the blasthead 25.

It has been previously stated that the heating system for the glasssheets is a circulating hot gas system, and the circulation bothsupports the glass sheets and assists in heating the glass sheets asthey pass along the support bed 20. To accomplished this, a longitudinalvertical wall 43 having spaced large circular openings adjacent theupper end thereof extends the length of the furnace, between theinsulated side wall 36 and the support bed 20. Between the wall 43 andthe insulated side wall 36 are a series of blowers, illustratedgenerally by the numeral 44, at spaced points along the length of thefurnace, each blower being positioned atone of the large openings in thewall 43. Preferably there should be at least one such blower for each ofthe zones 1 through 14 for optimum circulation of the gases within thefurnace 24. Wall 43, which constitutes a baflie is provided with aseries of apertures or perforations 45 at the lower portion thereof, theperforations being below the level of the support bed 20. With theblowers 44 operating and the gases in the furnace 24 above the bed 20being brought up to temperature by the burners 41, the gases will becirculated by the blowers 44 through the space between wall 43 and theinsulated side wall 36 and blown through the perforations or apertures45 in the baflie wall 43. The gases then flow into the plenumundernearth thebed and up through the perforations in the support bed 20to float and heat the glass sheets in a manner to become hereinaftermore apparent. Suitable baffle means 46 are located adjacent and belowthe front edge of support bed 20 to direct the flow of gases through theperforations in the support bed. A second baffle 47 between the verticalwall 43 and the bed 20 prevents the flow of gases past the bed. Verticalgenerally -L shaped 'baflie plates 48 (see FIGURES 3 and 5) extendingtransverse of the furnace are spaced every ten feet to separate the heatzones. Such baflie plates have an upper leg which extends from the topto the bottom of the blower chamber, i.e., the space between Wall 43 andthe insulated side wall 36, and a bottom leg which extends laterallyfrom the bottom perforated portion of wall 47 to the battle 46, andvertically from the insulated bottom wall 35 to the underside of the bedwhich is supported by rows of spaced posts 52 and 53 (see FIGURE 4).Hence, the furnace shown has a total of fourteen blowers, one at themiddle of each of the fourteen zones, the vertical baffles 48 separatingthe zones. The blowers are made of a high heat resistant metalsufficient to withstand upwards of 1500 F. and the electric motor drivemeans (not shown) for the blowers are located outside the furnace out ofthe high heat.

In operation, the blowers pull hot gases from the upper part of thefurnace, and route these gases to the plenum underneath the bed fromwhence they are forced by the pressure from the blower up throughperforations in the bed, thereby floating and heating the glass sheets.Then the gases circulate to the upper part of the furnace forrecirculation as described.

It will be apparent from the foregoing that the glass sheets passingalong the support bed 20 will be heated by heat from the burners 41 aswell as by the gases circulated by the blowers 44 through the supportbed 20. Since these gases also supply the flotation and support for theglass sheets, it is important that regulation means be provided for theblowers 44 to regulate the flow rate and thus the proper flotation ofthe glass sheets over the bed 20. For these purposes, suitable shuttersor doors 49. and 50 are provided for each blower. The shutters 49 and 50are pivotally secured as at 51 to the wall 43 or any other suitablestructure and are of semi-circular shape, as best illustrated in FIGURE3. The shutters are operable to partially close off the opening in thewall 43 leading to It has now been explained that the glass sheets 30are floated along the length of the support bed 20 by means of gasescirculated and recirculated from the interior of the furnace throughperforations in the support bed formed of ceramic section 31.

In the portion of the support bed 20 at the first part of the furnace24, that is, from zone 1 to the middle of zone 10, the bed sections 31may be generally rectangular flat sections approximately 30 inches longand of the desired width. Each of the sections in zones 1 through 9 isprovided with a plurality of perforations to permit gas flow upwardlytherethrough. FIGURE 6 is a perspective view of a typical bed section31a in this portion of the furnace and illustrates the. perforations 54formed therethrough. It has been found that for optimum flotation of theglass sheets over this section of the bed, the perforations preferablybe about Ax-inch diameters and spaced one-half inch apart laterally ofthe bed and three-quarters of an inch apart longitudinally of the bed.The perforations in adjacent transverse rows are staggeredlongitudinally such that every fifth row repeats the pattern and the/s-inCh stripe of impact of gas from each perforation on the glasssheets moving thereover slightly overlaps the strips from longitudinallyslightly offset neighboring perforations to afford uniform support andheating.

The hot combustion product gases circulated by the blowers 44 pass upthrough the perforations 54 to the top surface 55 of each section. Withthe glass sheet 30 disposed above the upper surface 55 and with thegases flowing through the perforations 54, a blanket of such gases willform over the surface 55 and on which the glass sheets 30 will float andbecome heated. The gases are permitted to flow across the surface 55,that is, between the surface 55 and the glass sheet 30, and out fromunderneath the glass sheets 30 at the edges thereof. The hot gasescontinue to circulate by means of the blowers 44 through the portion ofthe furnace containing the burners 41 and again to the underside of thebed section 31a. The flow rate of the gases caused by the blower 44 andthe size of the apertures 54 are such as to provide a suitable volume ofgas between the glass sheet 30 and the upper surface 55 to float theglass sheet thereover. Such volume of gas is at a relatively lowpressure; it has been found that pressures in the neighborhood of oneinch to two inches of water column pressure in the plenum in thisportion of the furnace is suflicient. The average pressure between theglass and the bed is equal to the weight of the glass per unit ofsurface which in the case of Aa-inch thick glass is As-inch water columnpressure. 'It has been found that a flow rate of approximately 7000cubic feet per minute per 25 square feet of bed is ample. With theproper amount of gas flow to generate the proper pressure, the glasssheets 30 will float across the surface of the bed portion 31a at adistance of somewhere between .04 inch and .25 inch in this section ofthe furnace. This relatively high float in this portion of the furnaceWhere the glass is rigid is advantageous in that it reduces thepossibility of glass contact with the bed. Also, as indicatedpreviously, when the cold glass sheets first enter into the furnacethere is likely to be a certain amount of warpage thereby increasing thepossibilities of glass contact with the bed which possibilities are, asstated above, reduced by using a higher float. Hence, extremely accuratecontrol of the bed surface is not essential in this portion of thefurnace. At the edges of the glass sheets the pressure is substantiallyzero and it will be obvious, therefore, that once the glass sheets reachdeformation temperature this system of support would not be feasible andhence another configuration is used, such configuration to be describedforthwith.

The hot gases emitted through the perforations 54 heat the glass sheetsup to deformation temperature by the time the sheets reach zone 10. Inthe section of the furnace including zones 10, 11, 12, 13 and 14, thatis, the last part of the fiat portion and all those portions where thecontour of the support bed is curved, the ceramic block sections 31btake on a perforation pattern and configuration such as is bestillustrated in FIGURES 7 through 9. In this portion of the furnace thesections 31b are provided with both inlet and exhaust perforations orapertures in a desired pattern. The inlet perforations 56 differ inthese zones of the bed 20 in that the upper portions adjacent the topsurface 57 of the block 31b are enlarged, as at 58, in a manner similarto countersinking. The inlet perforations 56 are arranged in spacedtransverse rows, as rows 59 and 60 in FIGURE 8, and disposed between therows are alternate rows of exhaust perforations 61. Exhaust perforations61, as best illustrated in FIGURE 9, extend partially through the blocksection 31b and communicate with transverse passages 62 extendingthrough the block section 31b from side to side; thus, perforations orpassages 61 and transverse passages 62 comprise channels communicatingwith the surface 57.

Such passages 62 open through the side of the block sections 31b abovethe bafides 47 in the furnace 24 and thus permit the exhaust gases to beexhausted directly into the furnace 24 for recirculation. The apparatus,therefore, utilizes one or more integral ceramic blocks 31 asillustrated in FIGURE 7 including a first upper surface 57 over whichfluid may flow to maintain a sheet of glass in spaced relationshipthereto. There is also included a second surface which defines thebottom of each block. The first and second surfaces are interconnectedby a plurality of sides and a plurality of discrete channels are spacedthroughout and communicate with the upper surface 57 and extend betweenand through at least one of the sides. The channels comprise a secondplurality of passages 62 extending completely through the block betweenand through the sides thereof and a third plurality of passages 61 whichextend into the block from the upper surface 57 to communicate with thepassages 62. The first plurality of discrete passages 56 are spacedthroughout the upper surface 57 among the passages 61 and extend throughthe interior of the block from the upper surface 57 to the second spacedsurface. The aggregate of the perimeters of the inlet perforations inthe plane of the bed surface is greater than the aggregate of theperimeters of the outlet perforations in the same plane such that when asheet of glass is positioned in close spaced parallel relationship tothe bed surface, the aggregate of the areas of imaginary walls extendingfrom the outlet orifices to the plane of the glass is less than theaggregate areas of imaginary walls extending from the inlet perforationsto the plane of the glass. The outlets function, therefore, to providerestrictive orifices for the gas flow and create a positive pressuresufiicient to support the glass. Hence, where the exhaust and inletperforations are all round and where the number of exhaust openings isabout equal to the inlet openings, as in the embodiment shown, thediameter of the exhaust perforations is smaller than that of the inletperforations.

It is important to note in FIGURE 8, therefore, that the diameter andtherefore the perimeter of the exhaust perforations 61 is smaller thanthat of the enlarged upper end of the inlet perforations 58. With aglass sheet spaced from the surface 57 of the section 31b, there isformed annular orifice 63 about the inlet perforations 58 which islarger than a similar annular orifice 64 formed between the glass sheetand the outlet or exhaust perfora tions 61. Since the inlet orifice 62is larger than the exhaust orifice 63 by reason of the larger perimeterof the inlet orifice, there will be a positive pressure above thesurface 57 sufiicient to maintain the glass sheet on the blanket of gasthus produced. In effect, then, there is substantially continuous gasblanket support for the glass sheets, the only voids in the gas blanketsupport being directly over the exhaust perforations. Summarizing, thesystem is functionally one wherein the gas support blanket is providedby restrictive exhaust perforations which create a back pressure whichincreases rapidly as the glass sheet settles toward or approaches thebed and the area of the annular orifices 64 decreases until the glasssheet reaches an equilibrium level above the bed. The inlet perforationsserve merely to supply low pressure gas to the constantly recirculatinggas blanket. As the distance between the glass sheet and the bedincreases, the back pressure around the outlet perforations decreasesnot only because of the resulting increase in the size of the orificesat the outlets, as described, but also because the aggregate of theinlet passages at their smallest diameter (i.e., below the flared upperends) are smaller than the aggregate of the outlet passages therebyrestricting the supply of low pressure gas from the plenum to thesurface of the bed.

Measurements show that the pressure in the enlarged generally conicallyshaped upper extremities of the inlet passages is not substantially lessthan the pressure in the plenum chamber. The plenum chamber pressure inthis zone of the furnace wherein both inlets and exhaust are used may beon the order of 1-8 to 2.5 inches water column pressure. The pressure ofthe gas support blanket between the bed and the glass sheet is aboutequal to the plenum pressure immediately over the inlet perforations andtapers off toward the exhaust orifices, the pressure directly over theexhaust orifices being zero; however, there is a positive presure oversubstantially the entire surface of the bed, except directly over theexhaust perforations, sufficient to support the glass sheet at itsequilibrium level as before described. Since the gases can circulatefrom the inlet perforations to nearby outlet perforations there is arelatively uniform average pressure through the central areas of theglass up to a narrow, about one-half inch, margin area adjacent to theedges of the glass from which area the gases can escape about the edgesof the glass. To compensate for this, the exhaust perforations 61decrease in size from the center of the section 31 to the edges thereof,as can be seen in FIGURE 8. This particular feature of the exhaustperforation pattern is more clearly described and is claimed in UnitedStates patent application Ser. No. 328,409, filed Dec. 5, 1963, in thenames of Harold A. McMaster and Arthur F. Van Zee and assigned to theassignee of the present invention.

Because the gas feed from the inlets need only be and is at lowpressure, there is little or no tendency of the hot gases being fed tocause localized distortions in the glass as is the case where highpressure jets impinge against the bottom glass surface.

Since heated gases are entering through the perforations 56, it wouldnot be desirable to have a continual axial row of inlet perforationssince this would produce an axial or longitudinal stripe of hot gasesagainst the under surface of the glass sheet 30. To avoid this problem,each inlet passage 56 in the longitudinal direction is offset slightlyfrom the preceding inlet passage 56. A suitable spacing has beendiscovered to be a repeat of every fifth row of inlet passages and toequally displace the succeeding perforations therebetween. In thismanner, the entire surface of the glass sheet 30 will be prop erlyheated without localizing or aligning heated sections thereof. Theoutlet perforations are likewise staggered, in the direction generallylongitudinally of the bed, each fifth row repeating.

The flow rate and the spacing and pattern of the perforations in theblock 31b in the zones 10 through 14 of the furnace are such as to makethe glass sheet 30 float at a closer distance to the support bed 20 thanduring the earlier section. The inlet perforations in block sections3112 have a diameter of one-eighth inch flaring outwardly to aboutthree-eighth inch at the top surface of the bed section. The depth ofthe flare is not critical but may be approximately one-quarter of aninch. The inlet passages below the flared upper ends are small incomparison to the outlet passages for the reason alluded to previously.The largest of the exhaust perforations are slightly less thanone-quarter inch in diameter. Both the inlet and exhaust perforationsmay be one and one-half inches apart longitudinally and one-half inchapart laterally. Further, as previously mentioned, the outletperforations may decrease in size from the center of the block sectionlaterally to the edges, the perforations at the edge being one-eighthinch in diameter and those between the center and the edge beingthree-sixteenths inch in diameter.

It has been found desirable to provide a flow rate of approximately 3500cubic feet per minute per 25 square feet of bed area and a gas presureof somewhat in the neighborhood of 1.8 to 2.5 inches of water pressurein the plenum section. Under such conditions, the glass sheets 30 willfloat lower or closer to the support bed than in the earlier sections,and at a distance of about .005 to .020 inch. Under such conditions theglass sheets more readily conform to the contour of the surface 57 ofthe bed sections 3117.

In between the high float section and the low float section of the bedas aforedescribed, is a float transition zone that extends from thebeginning to the middle of zone 10 of the furnace. Such transition zonebrings the glass sheets 30 from the high float condition to the lowfloat condition in a smooth and gradual manner. The transition zoneaccomplishes this by means of a gradual increase in the number ofexhaust perforations per unit of bed length, from none at the beginningof Zone 10 to a full complement of exhauts at the middle of zone 10.This is more clearly described and shown in United States patentapplication Ser. No. 3 09, filed Dec. 1963, in the names of Harold A.McMaster and Arthur F. Van Zee and assigned to the assignee of thepresent application.

There is a second bed transition zone, that being the transition fromflat to curved shape. It is important that this curvature transitionoccur in such a manner that no portion of the glass sheet 30 engages ordrags on the surface of the support bed 20. Keeping in mind that theglass sheet 30 is semi-rigid and is floating quite close to the bed, andthat it is the force of gravity which causes the glass sheet to deforminto the curved condition following the contour of the support bed 20,it will be seenthat if the beginning of the transition is too abrupt, itis possible for the center of the edge of the glass sheet, adjacent thechain conveyor, to hit or scrape the edge of support bed 20. Also, if inthe remainder of the transition the rate of curvature change is toorapid, there can be nonuniformity in the spacing of the sheet from thebed due to the inability of the sheet to bend rapidly enough to conformto the changing curvature, and this can result in nonuniformity of thegas support blanket over the bottom surface of the glass. If this occursthe glass sheet can drop to the point where the middle of the sheetadjacent the bed centerline contacts and drags on the bed. To attain thecurvature transition in the shortest possible distance and with theleast possibility of scraping or pressure nonuniformity problems asaforesaid, it is highly advantageous to shape the bed curvaturetransition zone such that the bed edges first fall away at a low rate,then at an increased rate, and then finally at a low rate. In otherwords, the rate of change in chord height should be such as to provide acurve similar to a sine 14 curve when plotted. This is disclosed indetail and covered in United States patent application Ser. No. 395,717,filed Sept. 11, 1964, now Patent No. 3,291,590, in the name of Harold A.McMaster and assigned to the assignee of the present invention.

From the foregoing it is apparent that the flotation of the glass sheets30 over the support bed 20 is accomplished by means of a flow systemresulting from the circulation of hot combustion gases from the furnacethrough a suitable blower assembly and through the support bed 20.Although the foregoing has been described with reference to a blocksection having a plurality of inlet perforations formed therethrough,this function may be accomplished in some other suitable manner. Forexample, it is possible to provide a porous ceramic block section whichwill permit free flow of gases therethrough. Such would be sufiicient tosupport the glass sheets on the desired blanket of gases provided, ofcourse, that the flow rate is proper. In order to provide exhaustoutlets, the same type of porous block section may be used and a seriesof nonporous pipes or tubes may be inserted or formed in the blocksection to communicate with the upper surface of the bed and lead to thedesired exhaust passages or to otherwise exhaust the gases from thesurface of the block section. Hence, the exhaust outlets by reason oftheir number and restricted size provide the required back pressure toform the gas support blanket, the gases being fed through the pores ofthe blocks serving to feed relatively low pressure gas at a support rateto maintain the blanket. Tubular inserts may be easily placed in theblock sections as they are originally molded, the inserts being ofsuitable size and shape to properly convey the exhaust gases frombetween the glass sheet 30 and the bed section. The tubular inserts,which constitute the exhaust perforations, can, if desired, extendslightly above the plane of the remainder of the bed, the upperextremities of the exhaust tubes being in a common plane or othersurface which, in effect, constitutes the plane or surface desired ofthe bed to provide the shape desired to the glass sheets. Otherconfigurations will be apparent to those having skill in the art afterhaving had reference to the specification and drawings of the presentinvention.

' T empering blasthead In a glass treating method and apparatus shown,the curved glass sheets are tempered immediately upon leaving thefurnace, the tempering blasthead being shown at 25 in FIGURE 1.Tempering of the glass has numerous well-known advantages and isaccomplished by rapidly and uniformly cooling the glass sheets afterthey have been heated to a particular temperature. Tempered glass ismost desirable in automobile installations because of the safetyfeatures involved. It is exceptionally strong; and if it does break, itdisintegrates to smooth rather than sharp-edge particles.

Referring in particular to FIGURES 10 through 1 the blasthead includesupper and lower beds, illustrated generally by the numerals 69 and 70,respectively. Beds 69 and 70 are provided with perforations or airpassages,

' convex and the upper bed 69 being concave, to receive the curved glasssheets 30 therebetween. Each of the beds 69 and 70 are provided withperforations of air passages, and each is provided with ductwork 71 and72 which leads from a suitable air blower apparatus, illustratedgenerally in FIGURE 1 by the numeral 73. Such apparatus may be any knowntype of construction suitable to provide a blast of room temperature airto the upper and lower beds 69 and 70 in accordance with normaltempering techniques.

As has been previously noted, it is intended that the glass sheets 30 befloated on the lower bed 70 as they pass through the blasthead 25. Toaccomplish this, the lower blasthead bed 70 is constructed as shown inFIG- URE 11 and includes a lower plate member 74 separated from theupper bed surface 76 by suitable perforated side walls 78 and 79.Disposed between the lower plate 74 and the upper plate 76 are aplurality of tubular members 80 which serve to convey the roomtemperature air therethrough and to the lower surface of the glasssheets 30.

A low float zone and then a high float zone are used in the particularblasthead shown. In the low float zone, the tubular members 80 aredisposed in rows transversely of the bed 70, as illustrated in FIGURE12, wherein rows '81 and 82 of inlet tubes 80 are in shallow transversegrooves 86 and are disposed in adjacent relation and separated by rowsof exhaust passages 83 and 84. The exhaust passages 85 in these rows areformed through the ridges intermediate the grooves in the upper platemember 76 and communicate with the hollow interior between the upperplate 76 and the lower plate 74. In the high float zone, there are notransverse grooves as in the low float zone.

In one method of operation it is desirable to transport the glassrapidly from the furnace to the blasthead and then suddenly applyquenching air to the entire area of the glass at once. To preventwarping or twisting of the soft glass it can be conveyed on a thin bedof air over the lower blasthead which is carefully aligned as acontinuation of the hot furnace bed. When the glass is fully inside theblasthead, the conveyor is slowed and the pressure is raised from about1 /2 inches to 5 inches water column or more, for rapid quenching ofboth top and bottom surfaces of the glass and it is desirable that theglass now float half-way between the upper and lower blastheads foruniform treatment. Thus it is necessary that the glass rise about /2inch or more when full air pressure is applied.

The grooves 86 FIGURE 13 prevent the glass from closing off the ends ofthe tubes 80 when the glass is floating low during the rapid transportfrom the furnace and the glass will float .010 inch to .060 inch abovethe ridges of exhaust holes 85 until the back pressure just supports theglass as described for the furnace bed. When the full quenching airpressure is app-lied, the back pressure in the exhaust holes exceeds theweight of the glass per unit of surface and the glass rises until theair escaping around its edges balances the pressure equal to the weightof the glass per unit of surface. Since the glass surfaces harden veryrapidly, very little warpage can occur. Additional portions of the lowerblasthead over which the glass always floats at a high level as iteontinues to move away from the furnace do not need the grooves 86. Thelow float, rapid transport sequence is not needed for smaller glasssizes which can be transported directly into high air quenchingpressures by slightly lowering the blasthead bed relative to the furnacebed. This is particularly true where the glass is precooled to about1150 F. in the last furnace zone to make it more rigid as it leaves thefurnace.

The upper bed 69 is generally similar to the lower bed having an upperplate 87 separated from a lower plate 88 by a plurality of air inlettubes 89 opening directly into the surface of the lower plate 88. Theupper bed has large exhaust holes 92. to keep the back pressure low soas not to force the glass downward. Plates 87 and 88 are joined byperforated side walls 90 and 91, to form a generally box-like structure,the space therein receiving the exhaust air from exhaust ports 92 androuting it out through the openings in the side walls. Ductwork 71conveys the cooling air from its source to the tubes 89 and thus to theupper surface of the glass sheet 30 disposed in the blasthead The flowthrough the tubular members 89 is such as to balance the flow throughthe lower tubular members 80 to prevent the glass sheet from engagingone or the other of the blasthead inner plates. With the proper controlof the flow rates this is not too serious a problem, and the glass sheetmay be easily balanced between the two plate members 88 and 76,respectively.

One means of controlling the flo wrate is to control the exhaust frombetween the plate members. To accotmplish this, suitable shutterarrangements, such as best illustrated in FIGURE 14, may be provided.Formed in the side wall 79 of the lower bed 7 0 and in the side wall 91of the upper bed 69 may be a series of rectangular ports 93 and 94,respectively. Disposed over ports 93 and 94 are slida'ble shuttermembers 95 and 96 respectively sliding in the brackets 97 and 98 in thelower member 70, brackets 99 and 100 in the upper member 69. Theshutters 95 and 96 may be slid in one direction or the other to open orclose the ports 93 and 94 leading to the interior of the beds 69 and 70.By thus controlling the exhaust flow, it is possible to properly controlthe position of the blass sheet 30 relative to the beds 69 and 70.

In the particular embodiment shown the first portion of the blastheadlower bed 70 has inlet perforations of about one-quarter inch indiameter, and spaced one inch apart laterally and one inch apartlongitudinally. The rows of inlet tubes are staggered in thelongitudinal direction such that every sixth row repeats. The outletperforations in bottom bed 70 are slightly smaller in diameter that theinlets and are spaced apart one-half inch laterally and one inchlongitudinally. The first portion of lower bed 70 is provided withgrooves 86 as aforesaid.

In the low float portion of the blasthead 25, the inlet perforations inthe upper bed have a diameter of about one-quarter inch and are spacedapart one inch in lateral and longitudinal directions. The outletperforations in this section of the upper bed are of fi-ve-eighths inchdiameter and are spaced apart on one-inch centers.

The perforation dimensions in the high float portion of blasthead 25 maybe the same as those for the first section.

Thus, the glass sheets may be transported through the furnace 24 forheating to deformation temperature prior to the tempering operation andupon leaving the furnace 24 pass directly into the blasthead 25. Theglass sheets 30 continue to float over the support bed and are cooledfrom the temperature at which they leave the furnace 24 to the propertemperature for removal from the blasthead 25 by the machine operator.

Conveyor system As has been previously pointed out, the support bed 20,extending through the furnace 24 and through the blasthead 25, isdisposed therewith at a slight angle, 12 in the embodiment shown,relative to the horizontal plane of the furnace. With the glass sheet 30floating on a blanket of gases above the support bed 20 and the blanketof gases being of substantially constant thickness, it is obvious thatthe glass sheet will have a component of weight force directed along theplane of the surface of the support bed 20. Due to this angularity andthis component of force, it is possible to provide a conveyor systemwhich will transport the glass sheets along the length of the supportbed with very light contact with the glass sheet 30. It will be furtherapparent that with the glass sheet 30 floating on the blanket of hotgases over the support bed 20, that very little force will be necessaryto transport or convey the glass sheet along the bed, and thus verylight contact in the direction of travel is all that is necessary.

Referring now to FIGURE 1 and FIGURES 15 through 21, the conveyor systemfor the glass sheets includes a guide rail 101 which is formed inaligned sections and extends alongside the lower edge of the bed for theentire length of the loading station, the furnace, and blasthead. Therail 101 may be suitably supported by posts 102, supported on thefurnace superstructure in a suitable rnanner. Riding on guide rail 101is a conveyor chain, indicated generally by the numeral 103, of typicallink and bearing rod construction having spaced members 104 dependingdownwardly therefrom at spaced is driven at a smooth uniform speedthrough the furnace and blasthead are described in detail and claimed inUnited States Patent application Ser. No. 478,521 filed July 15, 1965,now Patent No. 3,282,447 in the name of Harold A. M cMaster and assignedto the assignee of the present invention.

Extending inwardly from the chain 103 toward the support bed 20, and atproperly spaced intervals therealong, are support feet, indicatedgenerally by the numeral 105. Each support foot 105 includes a lowerplate member 106 which is supported on the support bed by flotation inthe same manner as the glass sheets 30. The plate members are providedwith upstanding ribs 107 to which are secured suitable rods 108extending and secured to the conveyor chain 103. The connection 109between the rods 108 and the ribs 107 is rather loose to allow somepivotal movement for purposes to be hereinafter described.

Extending upwardly from the inner edge of lower plate 106 issubstantially vertical plate member 110 provided with a series ofvertical lands and grooves 111 and 112, respectively. It is desirablethat the face of plate member 110 be as perpendicular as possible to theplane of the glass sheet 30 disposed thereagainst, and the glass sheet30 with its component of weight force in the direction of its surface,lightly engages the lands 111 on the upstanding plates 110. The slightfrictional engagement of the plate members 110 with the glass sheets 30is sufficient to convey the glass sheets through the furnace 24 andblasthead along with the chain 103. Extending outwardly from the topedge of the plate members 110 may be spaced tabs 113 which serve as astop means to prevent extreme upward movement of the glass sheets 30.Normally, however, the glass sheets do not engage the tabs 113 but areengaged with the upstanding plates 110 toward the lower edge thereof.

Extending outwardly from the rod members 108 are plates 114 which aresecured to the rod members 108 and to the chain 103 to properly directthe rod members 108 toward the interior of the furnace 24. Such plates114 maintain the precise angularity of the rod members relative to thechain 102 that is desirable in the installation. The plate members 114also serve to structurally maintain the rod members on the chain 103.

As indicated in FIGURE 18, the support feet 105 engage the glass sheets30, one at the forward end of the sheet and the other at the rearwardend of the sheet. If more support is necessary for the glass sheets 30,or if the glass sheets are of extreme length, it may be desirable toprovide additional support feet 104, located as' necessary for supportof the glass.

As illustrated in FIGURES 18 and 19, the glass sheets supported by thefeet 105 come out of the furnace 24 and blasthead 25 with a curvatureabout the longitudinal axis of the glass sheets 30. This is accomplishedby spacing the front support foot the same distance from the chain 103as the rear support foot, thus having the edge of the glass sheet 30parallel to its longitudinal center line. However, if it is desired toform glass sheets with a cylindrical curvature about an axis at an angleto the edge of the glass, this can be conveniently accomplished with theapparatus of this invention, as is illustrated in FIGURES 20 and 21. Asshown in these figures, the glass sheet has a curvature about a centerline angularly disposed relative to the central axis of the glass sheet.This is accomplished by having the distance of the front support foot105 from the chain 103 greater than is the distance of the rear supportfoot, as illustrated in FIGURE 20. Under such conditions, the glasssheeet 30 will be forced to fioat along the support bed 20 obliquely ofthe longitudinal axis of the support bed, and thus the desired curvatureand axis of curvature are obtained. Where considerable angularitybetween the axis of curvature and the longitudinal axis of the sheet isdesired, it may be advantageous to provide an extension on the rear footto engage the rear edge of the glass and thereby insure against theglass sheet slipping from the support feet,

within the furnace. It will be apparent that any axis of curvature maybe provided by the combination of support foot location and the surfacecontour of the support bed 20.

As indicated above in conjunction with the tempering operation, theconveyor can be of constant speed or it can be of variable speed so thatthe glass sheets can be moved relatively rapidly into the blasthead andthen slowed down within the blasthead. Of course, where a singlevariable speed chain is used this will mean that the sheets within thefurnace also move at varying speeds. In one method of operation, theglass sheets are sent through the apparatus in spaced pairs, theconveyor speed changes being sequenced such that as a pair of sheets isbeing moved into the blasthead at slightly increased speed, spaced pairsof sheets within the furnace are fore and aft of but not directly overthe curvature transition Zone. Of course, other arrangements can be usedif desired. For example, a separate higher speed conveyor chain can beused for the blasthead, such chain being cooperative with that throughthe furnace so that the glass sheets are transferred from the one to theother at the end of the furnace. Where this system is used it isdesirable that means be provided to preheat the support feet on theblasthead chain before they come in contact with the hot glass lestchill cracks develop in the sheets when contacted by such support feet.

To inhibit the flow of cool air into the furnace from the blasthead andhot gas into the blasthead from the furnace, a reciprocable door can beprovided between the furnace and blasthead as indicated in brokenoutline at 119 in FIGURE 1. Such door can be raised to allow passage ofone or more glass sheets into the blasthead, and then lowered again bysuitable means cooperative with the chain or the chain drive means.

Loading station In order to load the glass sheets 30 into the furnace24, a suitable loading station (see FIGURE 1) is provided, such loadingstation including a bed section made of aluminum or the like and havinga plurality of perforations 116 formed therethrough. A suitable airsupply system (not shown) within the housing 117 supporting the loadingbed section 21 provides a flow of air through the perforations 116 tofloat the glass sheets 30 thereover. In practice, the operator may takea glass sheet and place it over the bed and against a properly spacedpair of support feet on the conveyor chain 103 which extends along theedge of the bed section 21. The glass sheet 30, as it approaches thesurface of the bed, receives the supporting air from the perforations116, and a blanket of air disposed between the glass sheet 30 and thesupport supports the glass sheet and carries it into the furnace 24 asthe conveyor chain moves therealong. In this portion of the bed support,only gas inlet perforations need be provided, the gas exhausting fromthe edges of the sheet of glass and outwardly into the atmosphere.Alternatively, suitable recirculating means may be provided at theloading station it such is desirable; and any suitable recirculationsystem may be provided consistent with the flow requirements and otherparameters necessary to support the glass sheet.

Thus, a method and apparatus for treating glass sheets is provided whichis extremely eflicient and economical in its operation and construction.The glass sheets are conveyed along a suitable support bed havingperforations formed therein, and a recirculating gas system providesboth support for the glass sheets and heat for the glass sheets as theyare conveyed through the furnace and the blasthead for the necessarytreating operations. The recirculating system includes a series ofblower devices which convey hot gases from the furnace to a point belowthe support bed and thence through the perforations therein to the undersurface of the glass sheet. Suitable regulation means are provided forthe amount of flow through the blower systems which are simple andeificient to operate and maintain.

The support bed itself is of such construction as to minimize to thegreatest extent possible the degree of expansion and contraction whichmight come about clue to the heating up and cooling down of the furnace.The manufacture of the support bed of non-metallic material having anextremely low coeflicient of thermal expansion and high thermal shockresistance, contributes to the precision and quality of the glass sheetstreated by the method and apparatus. The position, location, and patternof the perforations in the support bed, in conjunction with thecirculating gas system, produces optimum flotation characteristics forsupporting the glass sheets as they pass through the furnace. Thesecombine to create a treated glass sheet of optimum properties andprecision without surface mars, scratches, or any other deformities.Tempered glass manufactured with the apparatus is particularlycharacterized by the marked reduction in striations as compared withglass sheets tempered with other types of apparatus. The contour of thesupport bed may be changed or altered depending on the type of operationand the shape of the glass sheets which are to be produced, and thevarious operations carried out within the furnace may be tailored tomeet the desired operation.

The conveyor system which moves the glass sheets through the furnace andthrough the blasthead is extremely simple in construction and operationand affords minimal contact with the glass sheets to avoid problems ofseriously marring the glass surface. The method completely eliminatesthe need for a high pressure float system which requires complicated andcumbersome equipment and generally results in surface distortions due tothe impingement of the high pressure hot gases onto the glass surface.

Numerous modifications and alterations to the structure and to thevarious parts of the furnace, blasthead, supporting bed, conveyor meansand the like, will become readily apparent to those having ordinaryskill in the art after having had reference to the foregoing descriptionand drawings. For example, whereas it is preferred to use a convexlycurved bed, a concave bed can be used if desired. Heating means otherthan gas burners can be used, for example, electrical heating elementswhere economics or other factors so dictate. If desired, the length ofthe bed can be reduced as, for example, by heating the glass up close toits deformation temperature by means other than the first high floatportion of the bed. Different blasthead structures can be used as candifferent glass loading station arrangements. Other modifications arealso possible. Hence, whereas the foregoing detailed description hasbeen chiefly related to one preferred embodiment of the invention, itwill be understood that various changes and alterations may be made allwithin the full and intended scope of the claims which follow:

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An integral ceramic block for use in an apparatus for treating glassand including a first surface over which fluid may flow to maintainglass in spaced relationship thereto, a second surface, said first andsecond surfaces interconnected by a plurality of sides, said ceramicbeing of a low coeflicient of thermal expansion, a plurality of discretechannels spaced throughout and communicating with said first surface andextending between and through 2% at least one of said sides, and a firstplurality of discrete passages spaced throughout said first surfaceamong said channels and extending through the interior of said blockfrom said first surface to said second surface.

2. An integral ceramic block as set forth in claim 1 wherein saidchannels include a second plurality of passages extending completelythrough said block between and through sides thereof and a thirdplurality of passages extending into said block from said first surfaceand communicating with said second plurality of passages.

3. An integral ceramic block as set forth in claim 2 wherein said blockhas four sides and wherein said second plurality of passages extendthrough said block between oppositely disposed first and second sides.

4. An integral ceramic block as set forth in claim 3 wherein said secondplurality of passages are parallel to one another and said thirdplurality of passages are perpendicular to said second plurality ofpassages.

5. An integral ceramic block as set forth in claim 4 wherein said firstplurality of passages are spaced among and parallel to said thirdplurality of passages.

6. An integral ceramic block as set forth in claim 5 wherein said firstand second sides are substantially parallel to one another.

7. An integral ceramic block as set forth in claim 6 wherein said firstsurface is curved in a direction extending between said first and secondsides.

8. An integral ceramic block as set forth in claim 7 wherein the thirdand fourth sides are substantially parallel to one another.

9. An integral ceramic block as set forth in claim 8 wherein said firstplurality of passages are arranged in a plurality of rows and said thirdplurality of passages are arranged in a plurality of rows.

10. An apparatus for treating glass sheet comprising: a furnace; a bedsupported in said furnace; means for moving glass sheet over said bed;said bed including at least one ceramic block having first and secondsurfaces interconnected by a plurality of sides, said ceramic being of alow coeflicient of thermal expansion, a plurality of discrete dischargechannels spaced throughout and communicating with said first surface andextending between and through at least one of said sides, and a firstplurality of discrete inlet passages extending through the interior ofsaid block from said first surface to said second surface and beingspaced from said channels throughout said first surface; and meansproviding fluid flow to said passages so that fluid flows over saidfirst surface and out said channels for supporting glass sheet on saidfluid over said bed as said glass sheet is moved over said bed.

11. An apparatus as set forth in claim 10 wherein said channels includea second plurality of passages extending completely through said blockbetween and through sides thereof and a third plurality of passagesextending into said block from said first surface and communicating withsaid second plurality of passages.

12. An apparatus as set forth in claim 11 wherein said bed is elongatedand includes a plurality of said blocks, each block having four sideswith said second plurality of passages extending through each blockbetween oppositely disposed sides, said oppositely disposed sidesdefining the longitudinal extremities of said bed.

References Cited UNITED STATES PATENTS 2,395,727 2/1946 Devol 65l823,223,501 12/1965 Fredley et al 65-25 DONALL H. SYLVESTER, PrimaryExaminer.

A. D. KELLOGG, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,338,697 August 29, 1967 Harold A. McMaster et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1 line 43 after "and" insert formed column 2 line 23 for"perculiar" read peculiar column 7 lines 52 and 55 for "uniformely" eachoccurrence read uniformly column 13 line 2 after "block" insert sectioncolumn 14 line 60 for "provided with perforations or air passages readarcuate in form, the lower bed 70 being line 63 for "of" read or column16 line 15 for "blass" read glass Signed and sealed this 10th day ofSeptember 1968 (SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

10. AN APPARATUS FOR TREATING GLASS SHEET COMPRISING: A FURNACE; A BEDSUPPORTED IN SAID FURNACE; MEANS FOR MOVING GLASS SHEET OVER SAID BED;SAID BED INCLUDING AT LEAST ONE CERAMIC BLOCK HAVING A FIRST AND SECONDSURFACES INTERCONNECTED BY A PLURALITY OF SIDES, SAID CERAMIC BEING OF ALOW COEFFICIENT OF THERMAL EXPANSION, A PLURALITY OF DISCRETE DISCHARGECHANNELS SPACED THROUGHOUT AND COMMUNICATING WITH SAID FIRST SURFACE ANDEXTENDING BETWEEN AND THROUGH AT LEAST ONE OF SAID SIDES, AND A FIRSTPLURALITY OF DISCRETE INLET PASSAGES EXTENDING THROUGH THE INTERIOR OFSAID BLOCK FROM SAID FIRST SURFACE TO SAID SECOND SURFACE AND BEINGSPACED FROM SAID CHANNELS THROUGHOUT SAID FIRST SURFACE; AND MEANSPROVIDING FLUID FLOW TO SAID PASSAGES SO THAT FLUID FLOWS OVER SAIDFIRST SURFACE AND OUT SAID CHANNELS FOR SUPPORTING GLASS SHEET ON SAIDFLUID OVER SAID BED AS SAID GLASS SHEET IS MOVED OVER SAID BED.